sfccxt/js/base/functions/throttle.js

A JavaScript / Python / PHP cryptocurrency trading library with support for 130+ exchanges

"use strict";

/*  ------------------------------------------------------------------------ */

const { now, sleep } = require ('./time');

/*  ------------------------------------------------------------------------ */

class Throttle {
    constructor (config) {
        this.config = {
            refillRate: 1.0,
            delay: 0.001,
            capacity: 1.0,
            maxCapacity: 2000,
            tokens: 0,
            cost: 1.0,
        };
        Object.assign (this.config, config);
        this.queue = [];
        this.running = false;
    }

    async loop () {
        let lastTimestamp = now ();
        while (this.running) {
            const { resolver, cost } = this.queue[0];
            if (this.config['tokens'] >= 0) {
                this.config['tokens'] -= cost;
                resolver ();
                this.queue.shift ();
                // contextswitch
                await Promise.resolve ();
                if (this.queue.length === 0) {
                    this.running = false;
                }
            } else {
                await sleep (this.config['delay'] * 1000);
                const current = now ();
                const elapsed = current - lastTimestamp;
                lastTimestamp = current;
                const tokens = this.config['tokens'] + (this.config['refillRate'] * elapsed);
                this.config['tokens'] = Math.min (tokens, this.config['capacity']);
            }
        }
    }
}

function throttle (config) {
    function inner (cost = undefined) {
        let resolver;
        const promise = new Promise ((resolve, reject) => {
            resolver = resolve;
        });
        if (this.queue.length > this.config['maxCapacity']) {
            throw new Error ('throttle queue is over maxCapacity (' + this.config['maxCapacity'].toString () + '), see https://github.com/ccxt/ccxt/issues/11645#issuecomment-1195695526');
        }
        cost = (cost === undefined) ? this.config['cost'] : cost;
        this.queue.push ({ resolver, cost });
        if (!this.running) {
            this.running = true;
            this.loop ();
        }
        return promise;
    }
    const instance = new Throttle (config);
    const bound = inner.bind (instance);
    // useful for inspecting the tokenBucket
    bound.config = instance.config;
    bound.queue = instance.queue;
    return bound;
}

module.exports = {
    throttle,
};

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